Effect of nanoclay on positive temperature coefficient to resistivity characteristics of high density polyethylene/silver‐coated glass bead composites

Positive temperature coefficient to resistivity characteristics of high density polyethylene (HDPE)/silver (Ag)‐coated glass bead (45 wt%) composites, without and with nanoclay, has been investigated with reference to HDPE/carbon black (CB) (10 wt%) composites. Plot of resistivity versus temperature of HDPE/CB (10 wt%) composites showed a sudden rise in resistivity (PTC trip) at ≈128°C, close to the melting temperature (T_m) of HDPE. However, for HDPE/Ag coated glass bead (45 wt%) composites, the PTC trip temperature (≈88°C) appeared well below the T_m of HDPE. Addition of 1 phr clay in the composites resulted in an increase in PTC trip temperature of HDPE/Ag‐coated glass bead (45 wt%) composites, whereas no significant effect of clay on PTC trip temperature was evident in HDPE/CB/clay composites. We proposed that the PTC trip temperature in HDPE/Ag‐coated glass bead composites was governed by the difference in coefficient of thermal expansion of HDPE and Ag‐coated glass beads. The room temperature resistivity and PTC trip temperature of HDPE/Ag‐coated glass bead (45 wt%) composites were found to be very stable on thermal cycling. Dynamic mechanical analyzer results showed higher storage modulus of HDPE/Ag‐coated glass bead (45 wt%) composites compared with the HDPE/CB (10 wt%) composites. Thermal stability of HDPE/Ag‐coated glass bead (45 wt%) composites was also improved compared with that of HDPE/CB (10 wt%) composites. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

PTCR characteristics of poly(styrene‐co‐acrylonitrile) copolymer/stainless steel powder composites

Positive temperature coefficient of resistivity (PTCR) characteristics of poly(styrene‐co‐acrylonitrile) copolymer (SAN)/stainless steel (SS) powder (80 wt %) composites prepared by melt‐mixing method has been investigated with reference to SAN/carbon black (CB) composites. The SAN/CB (10 wt %) composites showed a sudden rise in resistivity (PTC trip) at 125°C, above the glass transition temperature (T_g) of SAN (T_g ≈ 107°C). However, the PTC trip temperature of SAN/SS (80 wt %) composites appeared at 94°C, well below the T_g of SAN. Addition of 1 phr of nanoclay increased the PTC trip temperature of SAN/CB (10 wt %) composites to 130°C, while SAN/SS (80 wt %)/clay (1 phr) nanocomposites showed the PTC trip at 101°C. We proposed that the mismatch in coefficient of thermal expansion (CTE) between SAN and SS played a key role that led to a disruption in continuous network structure of SS even at a temperature below the T_g of SAN. The dielectric properties study of SAN/SS (80 wt %) composites indicated possible use of the PTC composites as dielectric material. DMA results showed higher storage modulus of SAN/SS composites than the SAN/CB composites. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Positive temperature coefficient to resistively characteristics of polystyrene/nickel powder/multiwall carbon nanotubes composites

Positive temperature coefficient to resistivity (PTCR) characteristics of polystyrene (PS)/Ni‐powder (40 wt%) composites in the presence of multiwall carbon nanotubes (MWCNTs) has been investigated with reference to PS/carbon black (CB) composites. The PS/CB (10 wt%) composites showed a sudden rise in resistivity (PTC trip) at ≈110°C, above the glass transition temperature (T_g) of PS (T_g ≈95°C). Interestingly, the PTC trip temperature of PS/Ni‐powder (40 wt%)/MWCNT (0.75 phr) composites appeared at ≈90°C (below T_g of PS), indicating better dimensional stability of the composites at PTC trip temperature. The PTC trip temperature of the composites below the T_g of matrix polymer (PS) has been explained in terms of higher coefficient of thermal expansion (CTE) value of PS than Ni that led to a disruption in continuous network structure of Ni even below the T_g of PS. The dielectric study of PS/Ni‐powder (40 wt%)/MWCNT (0.75 phr) composites indicated possible use of the PTC composites as dielectric material. Dynamic mechanical analysis (DMA) and thermogravimetric analysis studies revealed higher storage modulus and improved thermal stability of PS/Ni‐powder (40 wt%)/MWCNT (0.75 phr) composites than the PS/CB (10 wt%) composites. POLYM. COMPOS., 33:1977–1986, 2012. © 2012 Society of Plastics Engineers     

PTCR characteristics of polycarbonate/nickel‐coated graphite‐based conducting polymeric composites in presence of poly(caprolactone)

The effect of poly(caprolactone) (PCL) on the positive temperature coefficient of resistivity characteristics of polycarbonate (PC)/nickel (Ni)‐coated graphite (40 wt%) composites was investigated. The PTC trip temperature of PC/Ni‐coated graphite composites appeared at 155°C. On addition of PCL to PC/Ni‐coated graphite composites, the PTC trip temperature reduced to 125°C, well below the T_g of the PC (∼147°C), as well as the PC/PCL (∼136°C) blend. It is noteworthy that the observed PTC effect for PC/PCL (8 wt%)/Ni‐coated graphite (40 wt%) composites is highly reproducible during many heating cycles. The coefficient of thermal expansion (CTE) of PC was increased in presence of PCL. Thus, the mismatch in CTE of the PC and Ni‐coated graphite at a temperature well below the T_g of PC was enough to disrupt the continuous network structure that increased the resistivity of the composites. Storage modulus of PC/PCL/Ni‐coated graphite composites was higher than PC/Ni‐coated graphite composites. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Resistivity‐temperature behavior and morphology of low density polyethylene/graphite powder/graphene composites

In this work, the positive‐temperature‐coefficient (PTC) effect of resistivity of low density polyethylene/graphite powder (45%) composites (LDPE/GP) in the presence of graphene before and after crosslinked was comparatively investigated by differential scanning calorimetry (DSC), X‐ray diffraction (XRD), scanning electron microscopy, Raman spectrum, and resistivity‐temperature test. The composites showed the repeatability of the PTC effect with heating cycles and a certain improvement in the room temperature resistivity. After crosslinked, the composites presented a higher PTC trip temperature at about 140°C than pure LDPE (T_m = 112°C), and stronger PTC intensity than room temperature resistivity (over 5 orders of magnitude). The results from DSC, XRD, and Raman spectrum indicated that the addition of graphene resulted in the gradual enhancement in the crystallization of LDPE matrix, which was the origin of the improvement of the PTC behavior of the composites. As a result, we could conclude that the additional conducting filler could improve the PTC effect of the conducting composite system. POLYM. COMPOS., 35:1453–1459, 2014. © 2013 Society of Plastics Engineers     

Effect of coefficient of thermal expansion on positive temperature coefficient of resistivity behavior of HDPE–Cu composites

Positive temperature coefficient of resistivity (PTCR) characteristics of (high density polyethylene) HDPE–Cu composites has been investigated with reference to the conventional HDPE–CB (carbon black) composites. Plot of resistivity against temperature of HDPE–CB composites showed a sudden rise in resistivity (PTC trip) at 127°C, close to the melting temperature of HDPE. However, the PTC trip temperature (98°C) for HDPE–Cu composites was appeared well below the melting temperature of HDPE. Addition of 1 phr nanoclay in the composites resulted in an increase in PTC trip temperature of HDPE–Cu composites, whereas no significant effect of nanoclay on PTC trip temperature was evident in case of HDPE–CB–clay composites. We proposed that the PTC trip temperature in HDPE–Cu composites was governed by the difference in coefficient of thermal expansion (CTE) of HDPE and Cu. The room temperature resistivity and PTC trip temperature of HDPE–Cu composites were very much stable upon thermal cycling. DMA results showed higher storage modulus of HDPE–Cu composites than the HDPE–CB composites. Thermal stability of HDPE–Cu composites was also improved compared to that of HDPE–CB composites. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Hot‐embossing experiments of polymethyl methacrylate across the glass transition temperature with variation in temperature and hold times

Hot‐embossing (HE) experiments were conducted on polymethyl methacrylate (PMMA) across its glass transition temperature from 92 to 142°C. The glass transition temperature (T_g) of the PMMA used in this study was ～ 102°C. The polymer samples were embossed to a depth of 0.8 mm (800 μm). The experiments were carried out at various temperatures for different hold times of 30, 90, and 180 sec during the embossing process. A few additional experiments were conducted at 142°C with cooling of the samples as well. The force required for embossing and the final depth of the embossed features were analyzed. Polymers, including PMMA, show significantly different material behavior around and above T_g. The same was seen in the aforementioned tests; the trends observed for the force as well as the final depth changed considerably around 122°C (T_g + 20). These findings will be used in developing material models for use in simulating the hot‐embossing process. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Aging behavior of optically transparent poly (methyl methacrylate) composites

The thermal aging between 25 and 115°C of hot pressed glass fiber reinforced poly (methy1 methacrylate)(PMMA) transparent composites was studied as a function of the temperature and time of hot pressing. Thermal aging at near the T_g of the PMMA matrix caused dimensional changes and a reduction in optical transmission and clarity. The reduction in transmission was attributed to gas bubbles that formed in the matrix, which may be due to the evaporation of residual MMA monomer or low T_g (∼ 75°C) polymer in the composites during aging. Thermal cycling between 25 and 100°C by eliminating low T_g of the PMMA matrix establishes the upper temperature limit to which the composite can be exposed without seriously damaging its optical properties.     

Effects of glass bead content and surface treatment on viscoelasticity of filled polypropylene/elastomer hybrid composites

The dynamic mechanical properties of A‐glass bead filled polypropylene (PP)/ethylene–propylene–diene monomers polymer (EPDM) ternary composites have been measured over a temperature range from −80 °C to 100 °C and at a fixed frequency of 1 Hz, using a dynamic mechanical analyser (DMA), to identify the effects of the filler content and its surface treatment with a silane coupling agent on the dynamic viscoelastic behaviour. The results show that the storage modulus (E′_c) and loss modulus (E ″_c) of these composites with 10% volume fraction of EPDM at 25 °C increase non‐linearly with increasing volume fraction of glass beads (ϕ_g). At the same test conditions, the E′_c value of the PP/EPDM filled with pretreated glass beads is higher than that of the uncoated glass bead filled PP/EPDM system, especially at higher ϕ_g, while the difference in E ″_c between both systems is very small. The mechanical damping for the former decreases with increasing ϕ_g, but the opposite is true for the latter. The glass transition temperature of these composites varies irregularly with ϕ_g. The dynamic complex viscosity increases nonlinearly with an increase of ϕ_g. In addition, the interfacial structure between the matrix and inclusions has been observed by means of a scanning electron microscope. © 1999 Society of Chemical Industry     

Preparation and thermal,electrical, and morphological properties of multiwalled carbon nanotubeand epoxy composites

Multiwalled carbon nanotube (MWCNT)/epoxy composites are prepared, and the characteristics and morphological properties are studied. Scanning electron microscopy microphotographs show that MWCNTs are dispersed on the nanoscale in the epoxy resin. The glass‐transition temperature (T_g) of MWCNT/epoxy composites is dramatically increased with the addition of 0.5 wt % MWCNT. The T_g increases from 167°C for neat epoxy to 189°C for 0.5 wt % CNT/epoxy. The surface resistivity and bulk resistivity are decreased when MWCNT is added to the epoxy resins. The surface resistivity of CNT/epoxy composites decreases from 4.92 × 10¹² Ω for neat epoxy to 3.03 × 10⁹ Ω for 1 wt % MWCNT/epoxy. The bulk resistivity decreases from 8.21 × 10¹⁶ Ω cm for neat epoxy to 6.72 × 10⁸ Ω cm for 1 wt % MWCNT/epoxy. The dielectric constant increases from 3.5 for neat epoxy to 5.5 for 1 wt % MWCNT/epoxy. However, the coefficient of thermal expansion is not affected when the MWCNT content is less than 0.5 wt %. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1272–1278, 2007     

Dynamic percolation phenomenon of poly(methyl methacrylate)/surface fluorinated carbon black composite

The electrical resistivity of polymer filled with conductive filler, such as carbon black (CB) particles, is greatly decreased by incorporating the conductive filler. This is called the percolation phenomenon and the critical CB concentration is called the percolation threshold concentration (Φ*). For CB particle–filled insulating polymer composite at lower than Φ*, the conductive CB network is constructed in the polymer matrix when the composite is maintained at a temperature higher than the glass‐transition temperature or the melting temperature of the polymer matrix. This phenomenon is called dynamic percolation and the time to reach the substantial decrease in resistivity is called percolation time (t_p). To investigate the relationship between the dynamic percolation process and the surface state of CB particles, we used three kinds of carbon black particles such as original carbon black (CB0) and fluorinated carbon black (FCB010 and FCB025)–filled poly(methyl methacrylate) (PMMA). It was observed that the dynamic percolation curves for CB0‐filled PMMA and FCB‐filled PMMA composites shifted to a shorter percolation time with increases in both the annealing temperature and the filler concentration. However, the dynamic percolation curves of FCB‐filled PMMA showed a gradually decreasing trend compared to that of CB0‐filled PMMA composites. The activation energy calculated from an Arrhenius plot of the t_p against the inverse of the annealing temperature was decreased by surface fluorine treatment. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1151–1155, 2003     

Extensional processing behavior of thermoplastics reinforced with a melt processable glass

This work was concerned with investigating the processing behavior of thermoplastics reinforced with a melt processable phosphate glass under extensional flows at temperatures used for forming and shaping operations. Injection molded blends consisting of polyetherimide (PEI) and polyphenylene sulfide (PPS) reinforced with 30‐60 wt% phosphate glass were exposed to uniaxial and planar deformation at temperatures above the T_g of the phosphate glass (234°C) to evaluate the effects on the morphology and mechanical properties of the composites. Tensile testing at elevated temperatures (250‐300°C) was used to evaluate the forming behavior and ascertain the conditions most suited for the deformation of the composite blends. A temperature approximately 35°C above the T_g of the P‐glass was found to offer conditions most conducive to the deformation of the PEI/P‐glass blends. The phosphate glass reinforced PEI was found to offer greater retention of properties and smoother surfaces than an E‐glass filled material when exposed to shearfree deformation similar to that seen in a process such as thermoforming. For PPS based composites, the application of planar shearfree deformation near the melting point of the PPS (≈︁ 283°C) resulted in the elongation of the phosphate glass phase which served to enhance the stiffness of the composite blends along the principal deformation direction.     

Surface treatment of cellulose fibers with methylmethacrylate for enhanced properties of in situ polymerized PMMA/cellulose composites

Cellulose micro/nanofibers (CNF), prepared from jute fibers were surface treated with methyl methacrylate (MMA) for better dispersion into poly methyl methacrylate (PMMA) matrix. PMMA/cellulose composites were prepared by in situ suspension polymerization technique. The surface treatment of CNF was confirmed by Fourier transform infrared spectroscopy (FTIR) and Nuclear magnetic resonance (NMR) analysis. MMA‐treated cellulose micro/nanofibers (MCNF) demonstrated improved affinity and dispersion in MMA monomer as well as in the PMMA/cellulose composites. Thermal properties of the cellulose composites were analyzed by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The glass transition temperature (T_g) of PMMA increased by nearly 19°C in the in situ cellulose composites compared to that of unreinforced PMMA as indicated by DSC. TGA showed increased thermal stability of the cellulose composites. Enhanced tensile properties as well as significantly lower moisture uptake were observed in the in situ prepared PMMA/cellulose composites. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39808.     

Morphology,resistivity, and thermal behavior of EVOH/carbon black and EVOH/graphite composites prepared by simple saponification method

Poly(ethylene‐co‐vinyl alcohol) (EVOH)/carbon black (CB) and EVOH/graphite (GP) electro‐conductive composites were prepared by saponification of poly(ethylene‐co‐vinyl acetate) (EVA)/CB and EVA/GP composites in ethanol/KOH solution. The electrical resistivity change and positive temperature coefficient (PTC) behavior of these composites were investigated. The volume resistivity of EVA/CB and EVA/GP composites was decreased with saponification time. It can be observed that EVA/CB10 and EVA/GP05 composites showed a significant reduction in resistivity after saponification for 1 h. With the increase in saponification time, PTC peak temperature of both composites was shifted at a higher temperature. Tensile properties, morphology, and thermal behavior of the prepared composites have been also evaluated using universal test machine, scanning electron microscopy, and differential scanning calorimetry, respectively. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Electrical and mechanical characteristics of composites consisting of fractionated poly(3‐hexylthiophene) and conducting particles

The dynamic viscoelasticity of fractionated poly(3‐ hexylthiophene)titanium carbide (P3HT/TiC) composites was examined with regard to their electrical characteristics. The elastic modulus (E′) at 0°C [i.e., near the glass‐transition temperature (T_g) of P3HT] increased with increasing TiC content of the composite. In particular, composites whose TiC content exceeded the threshold concentration showed a high E′. This was caused by the high E′ of TiC and the strong interaction between TiC and P3HT. When the sample was heated above the T_g, E′ decreased rapidly and an increase in the loss tangent appeared near the T_g of P3HT. Mechanical loss was caused by friction between TiC and P3HT. The change in mechanical characteristics affected the electrical conductivity. When the TiC content of the composite approximated to the threshold concentration, a significant change in mechanical characteristics took place, so that a large positive temperature coefficient (PTC) effect was observed near the T_g. To explain the PTC phenomenon, we propose a model of conductive pathway for P3HT/TiC. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1429– 1433, 2002     

Synthesis of polyglutarimides from p(methyl methacrylate) and cyclohexylamine. I. Influence of working conditions on imidization reaction

Over the last 50 years methacrylic polymers, especially poly(methyl methacrylate) (PMMA), have reached a noteworthy place in world polymer production. However, for special applications that require thermal properties, polycarbonates take the place of PMMA because of the latter's low glass transition temperature (T_g) of 105°C. The aminolysis reaction of PMMA with cyclohexylamine in xylene was studied to obtain a polyglutarimide exhibiting higher T_g values. The mechanism involving aminolysis and further amidization of ester groups was correlated with the experimental characterization of all the species created during the reaction. Poly(N‐cyclohexylacrylamide) and polyglutarimide (prepared from this precursor) were prepared in order to determine the special characteristics of these model compounds by FTIR. This method abled the quantification of ester, amide, acid, and imide groups. This aminolysis reaction was optimized (190–250°C; ratio of constituents, 0.5: 3) by spectroscopically following the different groups and monitoring the increase of the T_g. Poly(N‐cyclohexyl glutarimide) (65%) containing amide groups (25%) and acid groups (10%) presents a T_g value of 195°C. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1876–1888, 2000     

Thermophysical properties of anhydride‐cured epoxy/nano‐clay composites

Polymer nano‐composites made with a matrix of anhydride‐cured diglycidyl ether of bisphenol A (DGEBA) and reinforced with organo‐montmorillonite clay were investigated. A sonication technique was used to process the epoxy/clay nano‐composites. The thermal properties of the nano‐composites were measured with dynamic mechanical analysis (DMA). The glass transition temperature T_g of the anhydride‐cured epoxy was higher than the room temperature (RT). For samples with 6.25 wt% (4.0 vol%) of clay, the storage modulus at 30°C and at (T_g + 15)°C was observed to increase 43% and 230%, respectively, relative to the value of unfilled epoxy. The clay reinforcing effect was evaluated using the Tandon‐Weng model for randomly oriented particulate filled composites. Transmission electron microscopy (TEM) examination of the nano‐composites prepared by sonication of clays in acetone showed well‐dispersed platelets in the nano‐composites. The clay nano‐platelets were observed to be well‐intercalated/expanded in the anhydride‐cured epoxy resin system. POLYM. COMPOS., 26:42–51, 2005. © 2004 Society of Plastics Engineers.     

Morphology,Resistivity, and PTC behavior of EVOH/CB composites prepared by solvent‐casting saponification and precipitation saponification

Poly(ethylene‐co‐vinyl alcohol)/carbon black (EVOH/CB) composites were prepared by a solvent‐casting saponification (‐D) and precipitation saponification (‐P) methods with a poly(ethylene‐co‐vinyl acetate)/CB (EVA/CB) toluene suspension. The effects of the CB content and saponification time on the morphology, electrical resistivity, thermal, and mechanical properties of EVA/CB composites were examined. The volume resistivity (ρ _v) of the EVA/CB‐D and EVA/CB‐P samples decreased significantly with increasing CB content and the percolation threshold of such composites was determined about 10 wt%. At 10 wt% of CB content, the ρ _v of EVA/CB‐D composite decreased significantly with the saponification time, whereas ρ _v of EVA/CB‐P composites did not change. As the saponification time increased, EVA/CB25wt% composites form cavity structure which CB is usually located in oval cavities larger than the particles themselves. This oval cavity structure almost resembles extruded high‐density polyethylene (HDPE)/CB composites. The morphology and PTC behavior of prepared composites were compared with those of HDPE/CB and the mechanism of PTC and NTC effects was discussed. POLYM. COMPOS., 38:1462–1473, 2017. © 2015 Society of Plastics Engineers     

Accelerant‐promoted free radical polymerization of methacrylates by stabilized nitroxide unimolecular initiators: synthesis and characterization

BACKGROUND: This investigation evaluates the effectiveness of initiator adducts for living and controlled polymerization of methacrylates, crosslinking of dimethacrylates and thermal stabilities of the resulting polymers. Adducts of 2,2,6,6‐tetramethyl‐1‐piperidinyloxy with benzoyl peroxide and with azobisisobutyronitrile were prepared and evaluated as stabilized unimolecular initiators for the free radical polymerization of methacrylate monomers using sulfuric acid as catalyst. The monomers used were methyl methacrylate, triethylene glycol dimethacrylate (TEGDMA) and ethoxylated bisphenol A dimethacrylate (EBPADMA). RESULTS: Successful polymerization was achieved at 70 and 130 °C with reaction times ranging from 45 min to 120 h. The dispersity (D) of poly(methyl methacrylate) (PMMA) was 1.09–1.28. The livingness and extent of control over polymerization were confirmed with plots of M_n evolution as a function of monomer conversion and of the first‐order kinetics. The glass transition temperature (T_g) for PMMA was 123–128 °C. The degradation temperature (T_d) for PMMA was 350–410 °C. T_d for poly(TEGMA) was 250–310 °C and for poly(EBPADMA) was 320–390 °C. CONCLUSION: The initiators are suitable for free radical living and controlled polymerization of methacrylates and dimethacrylates under mild thermal and acid‐catalyzed conditions, yielding medium to high molecular weight polymers with low dispersity, high crosslinking and good thermal stability. Copyright © 2008 Society of Chemical Industry     

Preparation and thermal properties of hybrid nanocomposites of poly(methyl methacrylate)/octavinyl polyhedral oligomeric silsesquioxane blends

A series of poly(methyl methacrylate) (PMMA)/octavinyl polyhedral oligomeric silsesquioxane (POSS) blends were prepared by the solution‐blending method and characterized with Fourier transform infrared, X‐ray diffraction, transmission electron microscopy, differential scanning calorimetry, and thermogravimetric analysis techniques. The glass‐transition temperature (T_g) of the PMMA–POSS blends showed a tendency of first increasing and then decreasing with an increase in the POSS content. The maximum T_g reached 137.2°C when 0.84 mol % POSS was blended into the hybrid system, which was 28.2°C higher than that of the mother PMMA. The X‐ray diffraction patterns, transmission electron microscopy micrographs, and Fourier transform infrared spectra were employed to investigate the structure–property relationship of these hybrid nanocomposites and the T_g enhancement mechanism. The results showed that at a relatively low POSS content, POSS as an inert diluent decreased the interaction between the dipolar carbonyl groups of the homopolymer molecular chains. However, a new stronger dipole–dipole interaction between the POSS and the carbonyl of PMMA species formed at the same time, and a hindrance effect of nanosize POSS on the motion of the PMMA molecular chain may have played the main role in the T_g increase of the hybrid nanocomposites. At relatively high POSS concentrations, the strong dipole–dipole interactions that formed between the POSS and carbonyl groups of the PMMA gradually decreased because of the strong aggregation of POSS. This may be the main reason for the resultant T_g decrease in these hybrid nanocomposites. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009